AT POVERTY POINT, Louisiana, a remarkable monument overlooks a bend in the Mississippi river. Built around 3500 years ago, entirely from earth, it consists of six concentric, semicircular ridges radiating out from a central “plaza”, together with five mounds. Mound A, the largest, towers 22 metres – the equivalent of a seven-storey building – over the lush floodplain. North America wouldn’t see another monument on this scale for 2000 years…

This article first appeared in New Scientist on 10 January 2018. To continue reading, click here (paywall).